The present invention relates to a vehicle occupant protection system for improving the crash safety of the vehicle.
In recent years, motor vehicles have been often fitted with a pretensioner device which positively increases the tension of the seat belt for restraining the vehicle occupant at the time of a crash and improves the protection of the vehicle occupant. The deceleration acting on the vehicle occupant who is restrained to the seat by a restraint device such as a seat belt starts rising only when the forward inertia force acting on the vehicle occupant at the time of the crash has started to be supported by the seat belt. As it is not possible to eliminate a certain amount of resiliency and slack in the seat belt, the deceleration of the vehicle occupant reaches a peak level only when the vehicle occupant has moved forward a certain distance under the inertia force and the elongation of the seat belt has reached its maximum extent. The peak value of the deceleration of the vehicle occupant gets greater as the forward displacement of the vehicle occupant under the inertia force increases, and is known to be substantially larger than the average deceleration of the passenger compartment of the vehicle body.
When the relationship between the vehicle body deceleration and the vehicle occupant deceleration is compared to the relationship between the input and output of a system consisting of a spring (vehicle occupant restraint device) and a mass (mass of the vehicle occupant), it can be readily understood that the maximum elongation and time history of the spring are dictated by the waveform (time history) of the vehicle body deceleration. Therefore, it can be concluded that the waveform of the vehicle body deceleration should be controlled in such a manner that not only the average deceleration acting on the vehicle body is reduced but also the overshoot of the vehicle occupant deceleration due to the elongation of the spring (vehicle occupant restraint device) is minimized.
In the conventional vehicle body structure, the impact energy is absorbed by a crushable zone, consisting of an impact reaction generating member such as side beams and gaps defined between various components, provided in a front part of the vehicle body, and the waveform of the vehicle body deceleration is adjusted by changing the resulting reaction properties by means of the selection of the dimensions and deformation properties of such parts. The deformation mode of the vehicle body other than the passenger compartment at the time of a crash may also be appropriately selected so that the deceleration of the passenger compartment of the vehicle body may be reduced, and the deformation may be prevented from reaching the passenger compartment. Such vehicle body structures are proposed in Japanese patent laid open publication (kokai) No. 07-101354.
It is important to note that the injury to the vehicle occupant at the time of a vehicle crash can be minimized by reducing the maximum value of the acceleration (deceleration) acting on the vehicle occupant which is dictated by the waveform (time history) of the vehicle body deceleration. It is also important to note that the total amount of deceleration (time integration of deceleration) which the vehicle occupant experiences during a vehicle crash is fixed for the given intensity of crash (or vehicle speed immediately before the crash). Therefore, as shown in FIG. 6 for instance, the ideal waveform (time history) of the vehicle body (seat) deceleration (G2) for the minimization of the vehicle occupant deceleration (G1) should consist of an initial interval (a) for producing a large deceleration upon detection of a crash, an intermediate interval (b) for producing an opposite deceleration, and a final interval (c) for producing an average deceleration.
The initial interval allows the vehicle occupant to experience the deceleration from an early stage so that the deceleration may be spread over an extended period of time, and the peak value of the deceleration to be reduced. According to a normal vehicle body structure, owing to the presence of a crushable zone in a front part of the vehicle and a slack and elongation of the restraint system such as a seat belt, it takes a certain amount of time for the impact of a crash to reach the vehicle occupant. The delay in the transmission of deceleration to the vehicle occupant must be made up for by a subsequent sharp rise in deceleration according to the conventional arrangement. The final interval corresponds to a state called a ride-down state in which the vehicle occupant moves with the vehicle body as a single body. The intermediate interval is a transitional interval for smoothly connecting the initial interval and final interval without involving any substantial peak or dip in the deceleration. Computer simulations have verified that such a waveform for the vehicle body deceleration results in a smaller vehicle occupant deceleration than the case of a constant deceleration (rectangular waveform) for a given amount of deformation of the vehicle body (dynamic stroke).
According to the conventional vehicle body structure, the vehicle body components of the crushable zone start deforming from a part having a relatively small mechanical strength immediately after the crash, and a part thereof having a relatively high mechanical strength starts deforming thereafter. As a result, the waveform of the crash reaction or the vehicle body deceleration is small in an early phase, and then gets greater in a later phase so that the vehicle occupant deceleration cannot be adequately reduced. To eliminate such a problem, it has been proposed to obtain a prescribed amount of reaction force by making use of the collapsing of the side beams and to maintain a stable reaction by providing a plurality of partition walls in the side beams (Japanese patent laid-open publication (kokai) No. 07-101354). However, such previous proposals can only maintain the vehicle body deceleration at an approximately constant level at most, and are unable to provide a more effective deceleration waveform.
To minimize the adverse effect of the resiliency of the seat belt, it is known to provide a pretensioner device in association with the seat belt to positively tension the seat belt at the time of a vehicle crash. According to another previously proposed structure, at least one of the anchor points of the seat belt is attached to a member which undergoes a movement relative to the remaining part of the vehicle which tends to increase the tension of the seat belt in an early phase of a vehicle crash. Such devices are beneficial in reducing the maximum level of deceleration acting on the vehicle occupant at the time of a vehicle crash, but a device capable of more precise control of the vehicle occupant deceleration is desired.
Referring to FIG. 9, the vehicle occupant deceleration G1 and vehicle body deceleration G2 correspond to the input and output of a transfer function representing a two-mass spring-mass system consisting of the mass Mm of a vehicle occupant, a spring (such as a seat belt), and a vehicle body mass Mv. More specifically, the vehicle body deceleration G2 can be given as a second-order differentiation of the coordinate of the vehicle body mass Mv with respect to time.
However, in an actual automotive crash, if a three-point seat belt is used, the shoulder belt portion of the seat belt which can be considered as a spring engages the chest of the vehicle occupant corresponding to the center of the vehicle occupant mass Mm so that the shoulder belt portion can be considered as consisting of two springs, one extending between the chest and shoulder anchor, the other extending between the chest and the buckle anchor.
If the seat belt is entirely incorporated to the seat, the shoulder anchor and buckle anchor move as a single body, and the two parts experience an identical deceleration. In such a case, it can be assumed that the seat belt can be given as a composite of two springs, and the deceleration acting on the shoulder anchor and buckle anchor is identical to the input to the two-mass spring-mass system or the vehicle body deceleration.
Now, suppose if the buckle anchor point is fixedly attached to the vehicle body while the shoulder anchor is capable of movement relative to the vehicle body as an example in which the two anchor points undergo different movements relative to the vehicle body. In such a case, because the shoulder anchor and buckle anchor experience different decelerations, the springs cannot be simply combined or the decelerations acting on the shoulder anchor and buckle anchor cannot be simply equated to the vehicle body deceleration.
Meanwhile, the external force acting on the chest wholly consists of the force received from the seat belt. Therefore, if the time history of the load acting on the seat belt in the direction of deceleration agrees with the time history of the spring load in the two-mass spring-mass system, the chest receives the same deceleration waveform as the response of the vehicle occupant mass of the two-mass spring-mass system to the optimum waveform of vehicle body deceleration. This enables the vehicle occupant to reach the ride-down state in which the vehicle occupant is restrained by the seat belt substantially without any delay and the relative speed between the vehicle body and vehicle occupant is zero (no difference between the vehicle occupant deceleration G1 and vehicle body deceleration G2).
To achieve a time history of the seat belt that produces such a state, it suffices if the time history of the average deceleration of the shoulder anchor and buckle anchor (or vehicle body) is equal to the optimum waveform of the vehicle body deceleration. Introducing the concept of the waveform of average vehicle body deceleration allows an identical result in reducing the vehicle occupant deceleration as controlling the vehicle body deceleration so as to achieve the optimum waveform to be achieved.
The early rise in the tension of the seat belt to apply the deceleration to the vehicle occupant from an early stage can be provided by a pyrotechnical actuator typically using a propellant. Pyrotechnical actuators are widely known in such applications as vehicle air bags and pretensioners. However, it was found due to the nature of its structure which relies on the generation of high pressure gas that such an actuator alone may not be able to produce a desired time history of the deceleration of the vehicle occupant. Also, not only the handling of pyrotechnical actuators requires a special care, but also the disposal of pyrotechnical actuators requires a special procedure. Based on such considerations, there are cases where the use of a pyrotechnical actuator is not desirable.
In view of such problems of the prior art, a primary object of the present invention is to provide a vehicle occupant protection system which can improve the protection of the vehicle occupant at the time of a vehicle crash for a given dynamic stroke or a deformation stroke of a front part of the vehicle body.
A second object of the present invention is to provide a vehicle occupant protection system which can maximize the protection of the vehicle occupant with a minimum modification to the existing vehicle body structure.
A third object of the present invention is to provide a vehicle occupant protection system which can maximize the protection of the vehicle occupant without increasing the weight of the vehicle body or taking up any significant amount of space in the passenger compartment.
A fourth object of the present invention is to provide a vehicle occupant protection system which can maximize the protection of the vehicle occupant without using any powered actuator.
According to the present invention, such objects can be accomplished by providing an automotive vehicle occupant protection system, comprising: a vehicle body including a chassis for supporting road wheels and a vehicle body main part mounted on the chassis in a relatively moveable manner in a fore-and-aft direction; a seat supported by the vehicle body main part; a seat belt provided in association with the seat and including an end attached to the chassis; means for engaging the vehicle body main part to the chassis under normal condition, and releasing the vehicle body main part from the chassis upon occurrence of a vehicle crash; and a bumper member provided on the chassis and adapted to collide with a stopper member provided on the vehicle body main part after a prescribed rearward travel of the chassis relative to the vehicle body main part.
Thus, upon occurrence of a crash, the chassis having a substantial mass starts decelerating, and moves rearward with respect to the remaining part of the vehicle body. This in turn causes the tension of the seat belt to increase, and the restraint on the vehicle occupant to increase. This is followed by the application of a reverse deceleration to the chassis or to the belt so that the initial sharp rise in the deceleration acting on the vehicle occupant is smoothly connected to the ride down state in which the vehicle occupant decelerates at the same rate as the vehicle body.
The chassis may consist of any part of the vehicle body, but typically provided with parts for supporting road wheels via wheel suspension systems. In the case of a front engine, rear drive vehicle, the chassis may centrally define a floor tunnel in which a propeller shaft extends. The buckle of the seat belt may be conveniently attached to a part of the chassis defining the floor tunnel.
The means for engaging the vehicle body main part to the chassis typically comprises a pair of members provided on the vehicle body main part and the chassis, respectively, which are frictionally engaged to each other. But other arrangements are also possible. For instance, a breakable member may be used for engaging the chassis and vehicle body main part to each other under normal condition. When a force exceeding a prescribed level which is expected to be produced at the time of a vehicle crash is applied to this breakable member, the breakable member ruptures or otherwise breaks so as to allow the chassis to move rearward with respect to the vehicle body main part.
To achieve a highly controlled, desired time history of deceleration, the vehicle body main part may be provided with a pair of side beams each having a front end located somewhat behind the front end of the chassis. Upon occurrence of a vehicle crash, initially, the chassis transmits the deceleration to the vehicle occupant via the seat belt, and the ride-down state is produced only when the chassis has traveled rearward by certain distance, and the relatively movement between the chassis and vehicle body main part has ceased. Immediately before or after this state is achieved, the side beams may jointly deform with the chassis in a controlled manner so as to control the maximum deceleration acting on the vehicle occupant. Typically, at least one of the bumper member and stopper is adapted to undergo a plastic deformation when the bumper member and stopper collide with each other so as to favorably control the time history of the deceleration acting on the vehicle occupant.